| Infrared transparent conductive film is a functional film with high infrared transmittance and high conductivity in the infrared band.In recent years,infrared transparent conductive film has been applied to the fields of reconnaissance surveillance,photoelectric sensors and transparent heaters,such as advanced multispectral reconnaissance pods,new solar cells,heating films,automatic body temperature monitors,etc.At present,producing visible-near infrared transparent conductive films with good mass production performance is not difficult and can basically meet the current needs.The coexistence of physical in-band transition absorption and carrier conduction leads to the difficulty of coordination between far-infrared transparency and conduction.The currently reported infrared transparent conductive materials generally suffer from the incompatibility between two properties.For example,materials such as carbon nanotubes,Ag nanowires,and CuAlO2can achieve either high conductivity or high infrared transmittance.Compared to these materials,the dielectric-metal-dielectric sandwich structure can combine the advantages of high optical transmittance of dielectric materials and high conductivity of metal materials,and is expected to achieve greater breakthroughs in the synergy of photoelectric properties.However,in the past research on sandwich structure,the academic community often used oxide materials such as ITO,AZO,and WO3as dielectric layer materials,which can only achieve visible-mid-infrared transparency despite their high conductivity.Up to now,far-infrared transparent conductive materials with sandwich structure have not been successfully developed.In the past studies,we found that bismuth selenide（Bi2Se3）has the special properties of fewer electrons and more central bonds and is a promising far-infrared transparent conductive material.However,the conductivity of this material is not ideal.In this paper,we designed and prepared for the first time a sandwich-structured composite film using bismuth selenide as the dielectric layer material,achieving the integration of high far-infrared transmittance and high conductivity.The main conclusions are summarized:（ⅰ）The infrared transmission spectrum of Bi2Se3films at different thicknesses were predicted by optical simulation calculation software and Bi2Se3（45 nm）films that met the requirements were screened.Bi2Se3（45 nm）films were prepared by magnetron sputtering equipment and their structure and photoelectric properties were characterized.The results show that the hexagonal Bi2Se3（45 nm）film has a conductivity of 304 S/cm and an average transmittance of 73.5%from 8 to 12μm.The good photoelectric properties of hexagonal Bi2Se3films are attributable low carrier concentration,higher carrier mobility and large relaxation time.At the same time,we determined the threshold thickness of Ti film to be 5 nm based on the changes in the square resistance of the Ti film with the help of a four-point probe instrument.In this study,material design criteria and candidate materials are provided to develop high-performance infrared transparent conductive films.（ⅱ）The infrared transmission spectrum of Bi2Se3/Ti（5 nm）/Bi2Se3composite films with different Bi2Se3thicknesses was predicted by optical simulation calculation software and the composite films with the highest infrared transmittance:Bi2Se3（20nm）/Ti（5 nm）/Bi2Se3（20 nm）were selected.The sample was prepared by magnetron sputtering equipment and characterized for its structural and photoelectric properties.The results show that the sample has a conductivity of 1175.8 S/cm and an average transmittance of 70.5%from 8 to 12μm.The excellent performance of Bi2Se3（20nm）/Ti（5 nm）/Bi2Se3（20 nm）composite films is attributable to the increase in conductive pathways,carrier injection effect and increased crystallinity of Bi2Se3films due to the embeded Ti films.In this study,a sandwich-structured infrared transparent conductive film more suitable for use in optical windows was designed.（ⅲ）In order to improve the conductivity of Bi2Se3films,three composite films with different structures were prepared by magnetron sputtering,namely Bi2Se3（20nm）/Ag/Bi2Se3（20 nm）,Bi2Se3（20 nm）/Ti/Ag/Bi2Se3（20 nm）and Bi2Se3（20nm）/Ag/Ti/Bi2Se3（20 nm）,and their photoelectric properties and structures were characterized.Bi2Se3（20 nm）/Ag/Ti/Bi2Se3（20 nm）,the photoelectric properties and structure were characterized.The results show that the Bi2Se3（20 nm）/Ti/Ag（9nm）/Bi2Se3（20 nm）composite films have a conductivity of 5988 S/cm and a far-infrared transmittance of 56.8%,which can effectively improve the conductivity of Bi2Se3films.The carrier concentration and carrier mobility of Bi2Se3（20nm）/Ti/Ag/Bi2Se3（20 nm）composite films are effectively improved by adding a Ti seed layer.In this study,a sandwich-structured infrared transparent conductive film with a sandwich structure is more suitable for infrared transparent heaters. |
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